How to Make Compost Tea for a Fast-Acting Organic Fertilizer That Gives Plants a Huge Boost of Nutrients

Compost tea is finished compost that’s steeped in water until the nutrients, bacteria, fungi, and beneficial organisms pull out into the liquid. It is a fast-acting alternative to dry soil amendments that require a long time to make a noticeable difference in your garden. You can use compost tea around plant roots or mist it onto leaves after just a day or two so plants can start getting the nutrients they need fast.

The quality of your brew lives or dies with the compost you use for your compost tea. It has to be fully broken down, dark and crumbly, with nothing recognizable left in it. Anyone still working out how to compost should nail that first, since unfinished compost could bring pathogens into your garden rather than the beneficial organisms you want.

But a single 5-gallon bucket batch of compost tea, made right, covers tons of ground and gives plants a huge boost. Here’s how to make your own compost tea at home.

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What Is Compost Tea?

Compost tea the liquid mixture made when you add compost or manure to water and let it steep. This DIY liquid fertilizer has many of the same beneficial microorganisms and nutrients found in compost. The thought is that by watering plants with this solution, plants have quick access to the best that compost has to offer.

In addition, some claim that regular use of compost tea can have the additional benefits of increasing the water retention of the soil, improving its fertility, reducing the need for chemicals in the garden, and reducing plant pathogens in some edible crops. But there are downsides of using compost tea that you should not ignore.

First, there are scant scientific studies backing up organic gardeners’ claims as to the positive effects of watering plants with compost tea. Since the composition of compost varies so widely, compost tea also varies, which makes careful and precise measurement of its true benefits difficult to ascertain.

In addition, compost is teeming with microbes. But some types of compost, like kinds that include manure, can create a tea with harmful, pathogenic microbes that do more harm than good. Bacteria like E. coli, Salmonella, and Listeria that cause foodborne illnesses can show up in improperly made compost and compost tea. That’s why it’s important to use only finished compost when making compost tea.

Benefits of Compost Tea

Regular compost does plenty of good when worked into soil, but a liquid compost tea gets into areas where dry soil amendments struggle to reach. They can add nutrients via leaf surfaces, deep into the root zones of plants, and cover wide areas without having to work in huge volumes of material all over the garden.

Nutrients that are already dissolved in water are available to roots immediately. That speed is important for plants with short growing seasons or for transplants that are still getting settled.

Microbes are really where compost tea earns its keep though. Beneficial bacteria and fungi from the brew settle into leaf surfaces and soil, outcompeting disease-causing organisms. Crowd these out before they establish and your plants have a lot less to deal with.

Regular application of compost tea builds up that beneficial microbe community over time, which improves moisture retention in the soil, more good biological activity, and reduced fertilizer dependency. It won’t rescue an absolutely wrecked soil on its own, but as part of a broader organic fertilizing routine it earns its place.

Best Types of Compost to Use

Not all compost brews equally. Fully mature compost is what works best – dark, crumbly, sweet-smelling, no woody bits or food scraps still in there.

Hot-composted material is the safest pick since high decomposition temperatures kill most harmful pathogens. Cold-pile compost doesn’t have that going for it. Bagged compost works fine, too, as long as it’s really finished. Worm castings make a particularly good base for compost tea and tend to produce a noticeably microbe-rich result.

Skip manure-based compost that hasn’t fully broken down. The pathogen risk on edible plants is real enough to not chance it. Plant-based compost teas can go on fairly often if needed. Manure-derived mixes are another matter entirely. Only use them heavily diluted and once a month at most.

Either way, aim for roughly one part compost to five parts water. A coffee-like color and an earthy rather than sharp smell means your compost tea is ready.

How to Make Compost Tea

Since compost tea has become more popular, some companies have begun manufacturing it and selling pre-made compost tea, like this one from Amazon. There are also compost tea bags, like these ones from Amazon, that you simply add to water to make your own natural fertilizer if you don’t have any compost on hand.

Many home gardeners, however, prefer to make their own compost tea. There are two main ways to do this. You can use either the non-aerated or aerated method. I’ll walk you through both methods.

Non-Aerated Method

The simplest compost tea recipe doesn’t require much in the way of equipment. A 5-gallon bucket and some finished compost is all you need. Rainwater or well water is best. But if tap water is all that’s available then let it sit out a few hours first to off-gas any chlorine, which can knock back the beneficial microbes your compost tea is trying to cultivate.

Add about 1 cup (240 mL) of compost per gallon (3.8 L) of water. You can throw it in loose or tie it up in a mesh bag. These reusable brew bags from Amazon work well and hold up across multiple batches. Steep your compost tea for 5 to 7 days, stirring daily. It will get funky-smelling and that’s fine. But if your compost tea smells sour that can be a sign something went wrong.

When the water goes dark and the smell settles into something earthy rather than sharp, strain it and use it. It’s good for soil drenching, though the aerated methods are often used to encourage microbial activity out of the same material if that’s the goal.

Aerated Method

Actively aerated compost tea, also known as AACT, requires an aquarium pump and air stones running through the water the whole time during steeping, which is what aerobic bacteria need to really take off. That gets the brew ready in 24 to 48 hours rather than close to a week.

You use the same setup with a bucket and the same compost ratio, but you add a continuously running pump, like this aquarium air pump kit from Amazon. Throw in a tablespoon of molasses to feed the microbes and speed things up. Kelp meal or fish hydrolysate work, too, for a richer result. You can get kelp meal and fish hydrolysate from Amazon.

Once the pump stops, use it within a few hours. Oxygen drops fast, aerobic organisms die back, anaerobic ones move in – which is the wrong direction entirely. Brew it, use it the same day, and clean the bucket well between batches.

How to Use Compost Tea on Plants

Apply compost tea as a soil drench around the root zone or as a foliar spray you mist onto the leaves. In either case, you should consider a few steps to keep your garden safe.

First, limit your use of compost tea to garden plants that are ornamental rather than those you intend to eat. This is the best preventative measure for avoiding pathogen exposure, since there is less chance of pathogen transfer into the food chain.

If you do want to apply compost tea to edible crops, don’t use it as a foliar spray. Instead add it to the soil. If you do this, you should:

• Wait 120 days from application to harvest.
• Time the harvest of those plants so that it falls 90 days away from other edible crops not fertilized with compost tea.
• Keep spray off edible plant parts that are eaten raw. Apply only to the soil.

Drenching large areas takes roughly 5 to 10 gallons per quarter-acre (19-38 L per 0.10 hectare). You can use a full-strength or diluted compost tea or dilute it up to a 10:1 ratio of water to compost tea, depending on how far the batch needs to go.

Wet the soil first because dry ground often sheds the liquid rather than letting it soak in. This garden pump sprayer from Amazon handles both the drench and foliar work cleanly and makes the job faster in larger gardens.

How Often to Apply Compost Tea

The best time to apply fertilizer is in the morning. This lets leaves dry before midday heat and microbes settle in. Ornamentals do well with a spray in late winter to early spring and then again when leaf buds break. For annual beds, a pre-planting application of compost tea gives soil microbes a head start.

Fungal or pest trouble? Apply as soon as you notice the problem and reapply with each regular watering. For all other regular scenarios, apply compost tea every two to four weeks throughout the growing season.

Seedlings can only handle a diluted solution of compost tea – around three parts tea to one part water. Established plants can take a full-strength dose without issue. Houseplants also require a diluted compost tea mixture, too. Dilute it by at least half and work it into your normal watering schedule rather than adding excess moisture.

Back off any synthetic fertilizers and pesticides where possible. Those knock back the microbial populations the tea is working to build. An organic liquid fertilizer from Amazon pairs well as a complement without undoing that microbial work. Regular compost additions and mulching on top of all that is also beneficial.

How to Store Compost Tea

You can store compost tea, but not for very long. If you opt to do so, select an airtight container that doesn’t allow light to penetrate. This can work for storage up to five days. For longer storage, you’ll need to refrigerate it and/or aerate it regularly with an aquarium pump or bubbler stone.

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